Arc lamp regulating circuit



Nov. 18, 1947. v M. A. HANKINS 2,430,929

ARC LAMP REGULATING CIRCUIT Filed March 1.7, 1947 INVENTOR.

MIA-YA. //4/v/(//v.s

w 'zv' Patented Nov. 18, N47

ARC LAMP REGULATING cmcorr Mariey A. Hankins, Los Angelcs, Calif., assignor, by mesne assignments, to Mole-Richardson 00., Los Angeles, Calif., a corporation of California Application March 17, 1947, Serial No. 735,157

6 Claims.

My invention relates to are lamp control circuits for stabilizing the light output of an illuminating arc.

In the operation of arc lamps, the most desirable characteristic to be maintained is uniformity of quality and quantity of light produced by the lamp. For example, in the illumination of motion picture sets, the most desirable characteristic is that of maintaining uniformity of quality and quantity of illumination so as to maintain the exposure density of the film at a relatively constant value.

Arc lamps that are generally used for illuminating purpose employ a machine for feeding carbon or other electrodes toward the arc-as the ends of these electrodes are consumed by the arc. Accordingly, stationary brushes are-disposed within the arc machine for supplying electric current to the electrodes regardless of the amount of movement of the electrodes. Generally two or more brushes are required for each electrode to obtain the desired current-carrying capacities. In spite of the fact that a ballast resistor is used with are lamps, there are variations in the arc current resulting in the undesired variations in the quantity and quality of light. I have discovered that these variations in illuminating characteristics are associated with variations of current in the brush circuits.

I have discovered further that the illumination of an arc may be effectively regulated by the insertion of resistors in the brush circuits of the arc electrodes. This control of the arc is much more effective than by the use of a ballast resistor alone, and is attributable to the fact that variations in resistance of the several brush circuits result in variations of current through the several brushes which have an adverse eifect upon the arc even though the overall arc current may remain substantially uniform.

It is therefore a general object of my invention to provide an improved illuminating arc.

Still another object of my invention is to provide an arc control circuit wherein a plurality of brushes supply current to each electrode, and the current through each brush is controlled .by an impedance.

Another object of my invention is to provide an illuminating arc circuit wherein brush resistors may supplement or supplant the normal ballast resistor generally used in arc circuits.

Other objects and advantages of my invention will be apparent in the following description and claims, considered together with the accompanying drawings, in which Fig. 1 is a schematic arc circuit wherein one of the arc electrodes is supplied with current through a plurality of brushes connected to fixed resistors; and

Fig. 2 is a schematic arc circuit wherein current is supplied to one of the arc electrodes through a plurality of brushes, the current of which may be controlled by variable resistors.

Referring to Fig. 1, two carbon rods it and I I may form the negative and positive electrodes, respectively, between which may be struck an are [2 which may be used for any desired purpose such as illumination. The negative electrode it! may be connected by a conductor is to any suitable source of supply represented schematically as a battery l4, although it will be appreciated that any other type of power source could be utilized, such as an electric generator. The positive electrode ll may be supplied with current through a plurality of brushes H3 maintained generally stationary within an arc machine, as is well known in the art. These brushes may be resiliently urged toward the electrode H by any suitable means (not shown) such as a spring so that a good electrical contact will be maintained with the electrode. Current may be supplied to the brushes I6 by a conductor ll connected to the opposite terminal of the power supply M, and the conductor ll may have two branches I'la and I'll) leading to the two brushes I6. Each brush circuit may include a resistor is provided especially in accordance with the invention, and the resistors may be connected by conductors I9 to their respective brushes.

In the operation of the circuit of Fig. 1 an arc may be struck between the electrodes til and II in any suitable manner, and thereafter will maintain itself. The current to the positive electrode l I will tend to divide itself between the two brushes l6 and thus produce approximately equal voltage drops across the resistors it which may be used as ballast resistors if desired. Itwill be appreciated, however, that minute diiierences of resistance between the two brush circuits may result in an increase in current of one brush circuit over the other. For example, the sliding of the electrode ll past the brushes it? will produce variations from time to time in the contact resistance between the brushes and the electrode. Accordingly the brush having the least contact resistance will tend to draw the heaviest current.

I have found that variations in the current through the brushes have a pronounced effect upon the illumination of the arc. This may be due to the fact that since the brushes are gen- 3 erally disposed closely adjacent to the end of the electrode, the magnetic field produced by the current passing through the brushes may extend to the area of the arc. Therefore when the brush currents are unequal so that the magnetic field of one does not balance the magnetic field of the other, the magnetic field f the brush carrying the most current predominates and: accordingly deflects the arc' to some extent, Chang-'- ing its illumination characteristics. The insertion of the resistors H3 in accordance with my invention, however, eliminates thisinfluencedue.

to variations in brush current by maintaining the brush currents approximately. equal at allxr. Accordingly the resistors l8 -should be:

times. of equal ohmic resistance for brushes of similar size. By making the resistance of .thBYIBSlStOIS l8 large compared to the contact resistance of the brushes, a change of brush contact resistance will not appreciably affect the resistance in the circuit of-that brush, thus maintaining the brush current substantially "constant; Thus-:the resistors l8 automaticallyregulate-thecurrent flow-- ing through the respective brushes by providing: ailsubstantially equal current in these brush circuits.

Shown in Fig. 2is a'modifi'ediform' of appara-- tus embodying my invention wherein the resistors are disposed in the brushcircuit ofitheznegative electrode, and further, the :resistors arevari able so as to'obtain any relative amounts .of current in the brushes.-' Accordingly anarc- Z'IImay be struck between a positive' electrodev 22'1and'a The. positive electrodeiz 2 negative electrode 23; maybe connected by'a conductor '24 'and aballast'resistor 26 to asuitable source of 'supply, such as a battery 27. A c0nductor -28 'may'be connected to the other terminal ofthe power supply and may have three b'ran'ches'z llm 28b; and 'ZB'c connected, respectively, to three-variable resistors 29? The other ends of the resistors 29 may be connected through conductors 31 to brushes 33 con= tacting the negative electrode-235'.

In operation, the arc 2| maybe struck in'any suitable manner and willthereafter maintain itself, The arc current distribution in the-brush circuits to the electrodes may be-precisely'regulated by means of theresistors-29 disposed inthe brush circuits particularly in accordance with the invention. The brushes 33 are preferably symmetrically arranged about the electrode-23when the resistors 29 are maintained at equal ohmic settings. If, however, there isan asymmetric arrangement of brushes 33, or" if the positive electrode 22 is disposed'at anangIe-With' respect to the negative electrode23; or for any other reason there is some asymmetrical aspect to the are as a whole, the currentthroughthe various brushes may be precisely'regulatedby'means'of the variable resistors 29% The resistors 29 act in the same manner astheresistors l8 ofFig; 1 to give a substantially constant drop in each brush circuit, despite the fact that there-'- might bevariations in thecontact'resistanceof the brushes. Thus the magnetic-fields generatedby the currents passingthrough the various brushes may-be precisely controlled; and 'the'illumin'ation' of the: arc accordingly may be carefully controlled.

From the combined-illustration of Figs. 1 and 2 'it'is obvious that my invention may beapplied' either. to the positivezelect'rode "or-'to the negative electrode; .or'to :both'; Further, itis obvious-that the invention may be employed either with or without a ballast resistor for the arc. Further, the resistors may be variable in any type of circult or combination. The only essential element is that there be a plurality of brushes for one or more electrodes, and that a current-controlling element be disposed in one or more of these brush circuits'to-regulate the relative currents between them.

It will be obvious to those skilled in the art that various types of impedance devices may be employed otherthan resistors. For example, inductors or coils could be employed in place of the resistors-to:effectively. choke down any increase of direct current'and to supply direct current when the current through the particular brush circuit momentarily. drops. Also, in the case of alternating current arcs, capacitors could be effectively utilized for the same purpose as the resistors illustrated.

From the foregoing itis obviousthat various modifications andequivalents-- could be utilized without departing from the true spiritand scope of? my invention. Accordingly Iv do" not limit, myself to theprecise disclosure,- nor'otherwise, except'by the terms of the followingclaims.

I claim:

1. An arccircuit comprising a-plurality of arc electrodes, parallelcircuitssupplying current to atleas+,- one '01 the electrodes; and current'regulatin'gdevices disposed: in' eachlof the. parallel circuits.

2. Anarc circuit comprising a pairxof electrodes, a plurality of wires connected in parallel to at least one ofthe electrodes,-and-.impedances disposed in each of theparallel wires;v

3. An arccircuit: comprising; a': pair'oft electrodesbetween which anrarc ma-y'be; struck, a plurality of brushes contacting at least one1of the electrodes so that'the electrode maybe moved relative thereto as itis'consumed by. the arc, a

source of electric current; parallel connections fromthe source tothe brushes, and-tresistors disposed in the-parallel connections.

4; An arccircuit comprising a; pairof' electrodes, at least; two brushes contacting one'of the electrodes, a source'of'current supply, parallel circuits connecting thesupplyand'the brushes,

and equal resistors placedi'in eachwbrushconnec tion' so that the currentto eachbrush will be maintained approximately-equal.

5; An arc circuit comprising a pair of electrodes between which an arc may be struck, a plurality" of brushes contacting at least one of thezelectrodes so that the electrode may be movedrelative thereto as it is consumed'by the arc, a source of: electric current; parallel connections fromrthesource'to: the brushes, resistors disposed inthe parallel connections;- and'aballast 'resistor connected in series between the supply'and one of the electrodes.

6. Ann arc circuit comprising: a pair of electrodes between which an-arc may bestruck, a plurality'of brushes contactingone' of the electrodes so that the electrode may be moved toward the are as the electrode is'consumed bythe arc, a source of current supply, conductors connecting one terminal of thesupply to the brushes in parallel, and variable'resistors disposed in each parallel conductor to'each brush, so that the'current through each brush may be-regulated'relative to the current in the other brushes;

MAXEY-A. HANKINS. 

